Microsoft Corp’s Skype has vanished from Apple Inc and Android smartphone app stores in China, becoming the latest victim in Beijing’s sweeping internet clampdown. The internet phone and video service was no longer available on Apple’s iOS or on popular local Android stores such as Xiaomi Corp’s, though it still functioned as of Wednesday. The Ministry of Public Security notified Apple that a number of voice-over-internet-protocol apps didn’t comply with local law and the US company subsequently removed them, a spokeswoman for the iPhone maker said. Those apps, which enable voice calls among other things, remain in place elsewhere.

It’s unclear why Skype, which has operated for years in China despite making little headway against more popular services like WeChat, was targeted. Under Xi Jinping, the Communist Party has tightened controls over online content and taken aim at messaging services in particular, requiring users to register their real names and threatening action against people who disseminate content deemed to threaten social stability. WhatsApp is periodically blocked in China, while the social network of its owner Facebook Inc isn’t accessible. Twitter and Google are similarly barred.

Microsoft said in a statement that Skype’s removal was temporary and it was working to get it reinstated as soon as possible, without elaborating. The Cyberspace Administration of China and Ministry for Industry and Information Technology didn’t respond to a faxed request for comment on the move, which the New York Times first reported. “Any instant messaging apps operating in China must follow the cybersecurity law, there’s no question about it,” said Zuo Xiaodong, vice-president of the China Information Security Research Institute, a government think-tank. “It goes without saying whose regulations need to be followed if a company’s own rules contradict China’s law—as long as it wants to continue to operate in the Chinese mainland.”

While Skype’s removal triggered a flurry of online complaints, it’s unlikely to inconvenience the vast majority of Chinese online users who’ve taken up more popular chat and calling services such as Tencent Holdings Ltd’s WeChat. As of Wednesday, rival messaging services from Signal to Telegram remained available for download. China is in the throes of the biggest crackdown on freedom of expression and media in the internet era. Foreign companies complain of restrictions that hamstring operations and favor homegrown players. Police are shutting businesses and arresting civilians on message groups as Beijing plugs more holes in its “ Great Firewall” blockade of blacklisted sites.

Xi has galvanized a nationwide machine in which corporations, cyber cops and automated systems police content to preserve the party’s seven-decade rule. As global giants from Alphabet Inc’s Google to Facebook Inc explore entry, they have to weigh the benefits of tapping the world’s biggest internet market against the fallout from appearing to back a repressive regime. Apple itself has come under fire, as critics accuse the world’s largest company of aiding and abetting censorship.

One of the key measures Beijing’s taken is a crackdown on virtual private networks, services that skirt censorship restrictions by routing web traffic abroad. Apple has removed 674 of such apps from its Chinese app store at the request of the local government, the iPhone maker revealed in a letter sent Tuesday to Democratic Senator Patrick Leahy of Vermont and Republican Senator Ted Cruz of Texas. Leahy responded by calling for Apple to push back against Chinese “suppression of free expression.” “We are convinced that continued engagement is the surest way to effect change,” Cynthia Hogan, Apple’s head of lobbying in the US, wrote in the letter. “We express our opinions about the impacts of laws and regulations forthrightly to policymakers.”